Lennox SLP98UHV Installation Instructions Manual page 19

Maximum Allowable Vent Pipe Length (in ft.) Without Insulation In Unconditioned Space
Winter Design
Vent Pipe
Temperatures1
Diameter
°F (°C)
2 in.
32 to 21
(0 to -6)
2-1/2 in
3 in.
2 in.
20 to 1
2-1/2 in.
(-7 to -17)
3 in.
2 in.
0 to -20
2-1/2 in.
(-18 to -29)
3 in.
1Refer to 99% Minimum Design Temperature table provided in the current edition of the ASHRAE Fundamentals Handbook.
2 Poly-Propylene vent pipe (PP) by Duravent and Centrotherm.
NOTE - Concentric terminations are the equivalent of 5' and should be considered when measuring pipe length.
NOTE - Maximum uninsulated vent lengths listed may include the termination(vent pipe exterior to the structure) and cannot exceed 5 linear feet or the maximum allowable
intake or exhaust vent length listed in table 5 or which ever is less.
NOTE - If insulation is required in an unconditioned space, it must be located on the pipe closest to the furnace. See figure21.
For Winter Design Temperatures Modulating High Efficiency Furnace
070
PVC PP
2
11 9
7
N/A
N/A
Conditioned
Space
TABLE 6
Unit Input Size
090
PVC PP
2
14 12
10 N/A
6 6
6 4
N/A N/A
Conditioned
Space
Pipe Insulation
Unconditioned
Space
FIGURE 21
Page 19
110
PVC PP PVC
2
18 15
N/A
12 N/A
8 8 13
8 6
N/A
N/A N/A
Exhaust
Pipe
Intake
Pipe
135
PP
2
N/A
13
N/A